Got it:
// Gets both automatic and manual groups:
(unique values of it) of ((values of headers "subject" of relevant fixlets whose (value of header "X-Fixlet-Type" of it = "ComputerGroup") of sites); (if exists ((settings of client) whose (it as string contains "__Group_0_" and it as string contains "=True")) then (following texts of substrings "__Group_0_" of preceding texts of substrings "=True" of (((settings of client) whose (it as string contains "__Group_0_" and it as string contains "True")) as string)) else "")
// Checks for a group matching regex:
exists ((unique values of it) of ((values of headers "subject" of relevant fixlets whose (value of header "X-Fixlet-Type" of it = "ComputerGroup") of sites); (if exists ((settings of client) whose (it as string contains "__Group_0_" and it as string contains "=True")) then (following texts of substrings "__Group_0_" of preceding texts of substrings "=True" of (((settings of client) whose (it as string contains "__Group_0_" and it as string contains "True")) as string)) else "")) whose (it as string as lowercase = (regex "win.*")))
Thanks for your help, Bill!
-chad